The invention relates to internal combustion engines, and more particularly to fuel-injected, two-stroke internal combustion engines.
It is known to use different inputs to control a fuel-injected, two-stroke engine at high and low engine speeds. In an engine operating with stratified combustion under part-load conditions, there is always excess air available to combine with the injected fuel. Engine power can therefore be controlled simply by varying the amount of fuel injected as a function of engine speed and throttle position. As a result, it is not necessary to determine with a high degree of accuracy the engine air flow at part load. However, as the load approaches wide open throttle and the combustion becomes less stratified, it is desirable to control engine power by varying the amount of fuel injected as a function of mass air flow. See, for example, U.S. Pat. No. 4,932,371.
U.S. Pat. No. 4,932,371 teaches that mass air flow can be derived either with a conventional mass air flow sensor within the intake manifold or by computer processing of a pressure signal produced by a pressure sensor within the crankcase. While the use of a conventional mass air flow sensor may be practical in an automotive application, it is not practical in a marine application. Water adversely affects the accuracy of a mass air flow sensor. It is therefore impractical to use mass air flow as the primary input for controlling the engine of an outboard motor.
U.S. Pat. No. 4,750,464 discloses a fuel injection system in which mass air flow is used to control the amount of fuel injected at all engine speeds. The amount of air coming into the engine is determined from the velocity and mass of the air. Velocity is determined by sensing the pressure drop across a venturi in the air intake manifold, and mass is measured by sensing air pressure and temperature. No throttle position sensor is used.